This invention relates to components which rotate and, more particularly, relates to a method and apparatus for imposing limits on the extent of rotation of a rotating component.
In some mechanisms having components which rotate, the components must rotate only within predetermined limits. These limits may fall within a range of up to 360 degrees, requiring some means to keep the rotation of the rotating component within the desired predetermined limits. Traditionally, stationary mechanical stops have been used to provide this function.
In the prior art, a set of stationary stops are often provided for setting limits to the extent of rotary motion of a rotating component. The rotating component may include a lug which protrudes outwardly and moves in a given path of revolution about the axis of rotation of the rotating component. Left and right stops are mounted to a stationary component adjacent the rotating component and extend across the path of revolution of the lug. When the rotating component rotates in one direction, the lug eventually hits one of the stops, preventing the rotating component from rotating any farther in that direction. When the rotating component reverses its direction of rotation, the lug eventually hits another of the stops, halting rotation of the rotating in the reverse direction. Thus, the stops limit the extent of rotational motion of the rotating component to less than 360 degrees.
A problem exists, however, when the rotating component must have a range of motion which is greater than 360 degrees. The traditional stops fail to provide a solution if the rotating component must have range of motion with predetermined limits greater than 360 degrees apart from one another. Consequently, a need remains for an arrangement that solves the aforementioned problem without introducing any new problems in its place.
A rotary motion limiting arrangement designed to satisfy the aforementioned need allows a rotating component to have a desired range of rotational motion within predetermined limits spaced apart by greater than 360 degrees and less than 720 degrees. For applications requiring only a single level of safety in limiting the rotating component to the desired range of rotational movement, the rotary motion limiting arrangement may utilize movable mechanical stops only. For applications requiring two levels of safety, the rotary motion limiting arrangement will utilize a plurality of electrical switches in conjunction with the movable stops. The electrical switches provide the first or primary level of safety while the movable stops provide the second or secondary level of safety.
In one embodiment of the invention, a rotary motion limiting arrangement comprises a stationary component, a rotating component with a first lug, a pair of stops and a link interconnecting the stops. The rotating component is rotatable in opposite directions relative to the stationary component and has a lug thereon movable along a path of revolution with rotational movement of the rotating component. The stops are mounted on the stationary component at angularly spaced locations about the rotating component and are movable between extended and retracted positions respectively across and outside of the path of revolution of the lug on the rotating component. The link which interconnects the stops is movable with the stops such that in response to contact of the lug with a stop during rotational movement of the rotating component in a first direction the stop is moved from the extended position to the retracted position and concurrently the other of the stops is moved from the retracted position to the extended position such that the lug continues past the one stop and stops at the other stop, thus establishing a limit to the rotational movement of the rotating component in the first direction. In response to contact of the lug with a stop during rotational movement of the rotating component in a second, opposite direction, the other stop is moved from the extended position to the retracted position and the one stop is moved from the retracted position to the extended position such that the lug continues past the other stop and stops at the one stop, so as to establish a limit to the rotational movement of the rotating component in the second direction. A range of limits to the rotational movement of the rotating component is thereby provided by placement of the stops at selected angularly spaced locations about the rotating component. Moreover, the opposite limits to the rotational movement of the rotating component are separated by greater than 360 degrees and less than 720 degrees from one another. The arrangement further comprises a pair of sleeves mounted on the stationary component and disposed at the angularly spaced locations about the rotating component. Each of the sleeves has an interior bore extending between opposite open inner and outer ends such that the inner ends of the sleeves are disposed adjacent to the rotating component and the outer ends of the sleeves are disposed remote from the rotating component. Each of the stops extends through the interior bore of a respective one of the sleeves such that an outer end of the stop protrudes from the outer end of one sleeve and is attached to the link, while an inner end of the stop is extendible and retractible relative to the inner end of the one sleeve upon movement of the stop relative to the rotating component.
In another exemplary embodiment of the invention, the rotary motion limiting arrangement comprises the above defined components and, in addition thereto, a second lug on the rotating component, a braking mechanism disposed adjacent to the rotating component, and a plurality of switches mounted to the stationary component and electrically connected to the braking mechanism. The first lug follows a first path of revolution with rotation of the rotating component while the second lug follows a second and different path of revolution with rotation of the rotating component. The stops and link function to establish a first set of opposite limits for the rotational movement of the rotating component. The switches are disposed adjacent to the link and the second path of revolution of the second lug on the rotating component, and are operable in response to contact with the link and the second lug during rotational movement of the rotating component in the first and second directions in order to establish a second set of opposite limits for the rotational movement of the rotating component, which are within the first set of opposite limits.
The plurality of switches includes first and second pairs of switches that are activatable between electrically off and on positions for electrically actuating a braking mechanism from a release condition to a braking condition relative to the rotating component, in order to mechanically halt rotation of the rotating component. Each of the first switches is disposed adjacent to one of the stops such that when the stops are in their extended positions the link does not contact the first switches, leaving the first switches in their off positions. When the stops are in their retracted positions, the link contacts the first switches, thereby actuating the first switches to their on positions. The second switches are disposed adjacent to the rotating component and at angularly spaced locations from one another. Each respective one of the second switches is also disposed closer to one of the stops than to the other of the stops and extends across the second path of revolution of the second lug on the rotating component such that the second switches are in their off positions when not contacted by the second lug and are actuated to their on positions when contacted by the second lug. When both the first switch adjacent to one of the stops and the second switch closer to the other of the stops are contacted respectively by the link and second lug on the rotating component, these switches are activated and the braking mechanism is electrically actuated from the release condition to the braking condition, halting the rotational movement of the rotating component.